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Bulletin  252 


December,  1923 


'   S 


Connecticut 
Agricultural  Experiment  Station 


NEW  HAVEN,  CONN. 


The  European  Red  Mite 


PHILIP  GARMAN 


Figure  1.     European  Red  Mite,  greatly  enlarged. 


CONTENTS 


Page 

History 103 

Nature  of  the  Injury 103 

Distribution 104 

Host  Plants..  .. 104 

Habits  and  Life  History 104 

Methods  of  Spread 106 

The  Different  Stages 107 

Description 107 

Difference  from  Other  Species .    107 
Number  of  Mites  Necessary  to 
Produce  Browning 108 


Page 

Varietal  Preferences 109 

Natural  Enemies 109 

Weather  Affecting  Abundance .   109 

Control  Measures 110 

Sprays  for  the  Winter  Eggs ...    110 

Summer  Sprays 116 

Spray    Burn   Resulting    From 

Lime-Sulphur  Sprays 122 

Summary    and    Recommenda- 
tions     123 

Literature 124 


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CONNECTICUT  AGRICULTURAL  EXPERIMENT  STATION 

OFFICERS  AND  STAFF 
December,   1923. 


BOARD  OF  CONTROL. 
His  Excellency,  Charles  A.  Templeton,  ex-officio,  President. 

James  H.  Webb,  Vice-President Hamden 

George  A.  Hopson,  Secretary Mount  Carmel 

Wm.  L.  Slate,  Jr.,  Director  and  Treasurer New  Haven 

Joseph  W.  Alsop Avon 

Charles  R.  Treat Orange 

Elijah  Rogers Southington 

Edward  C.  Schneider Middletown 

STAFF. 
E.  H.  Jenkins,  Ph.D.,  Director  Emeritus. 


Administration. 


W.  L.  Slate,  Jb.,  B.Sc,  Director  and  Treasurer. 
Miss  L.  M.  Bratxtlecht,  Bookkeeper  and  Librarian. 
Miss  J.  V.  Behgee,  Stenographer  and  Bookkeeper. 
Miss  Maet  Bradley,  Secretary. 
William  Veitch,  In  Charge  of  Buildings  andjGrounds. 


Chemistry. 

Analytical  Laboratory. 


Biochemical 

Laboratory. 


Botany. 


E.  M.  Bailey,  Ph.D.,  Chemist  in  Charge. 
R.  E.  Andeew,  M.A. 

Ow^nSLEnTan  1   **™tant  Christ8' 

Haeby  J.  FlSHEE,  A.B.         J 
Fbank  Sheldon,  Laboratory  Assistant. 
V.  L.  Churchill,  Sampling  Agent. 
Miss  Mabel  Bacon,  Stenographer. 

T.  B.  Osboene,  Ph.D.,  Sc.D.,  Chemist'Jn  Charge. 


G.  P.  Clinton,  Sc.D.,  Botanist  in  Charge. 

E.  M.  Stoddard,  B.S.,  Pomologist. 

Miss  Florence  A.  McCormick,  Ph.D.,  Pathologist. 

G.  E.  Graham,  General  Assistant. 

Mrs.  W.  W.  Kelsey,  Sec.etary. 


Entomology. 


W.  E.  Britton,  Ph.D., Entomologist  in  Charge;  State  Entomologist . 

B.  H.  Walden,  B.Agr.         } 

M.  P.  Zappe,  B.S.  \  Assistant  Entomologists. 

Philip  Gasman,  Ph.D.         J 

John  T.  Ashworth,  Deputy  in  Charge  of  Gipsy  Moth  Work. 

R.  C  Botsfoed,  Deputy  in  Charge  of  Mosquito  Elimination. 

Miss  Gladys  M.  Finley,  Stenographer. 


Forestry. 


Walteb  O.  Filley,  Forester  in  Charge. 
A.  E.  Moss,  M.F.,  Assistant  Forester. 
H.  W.  Hicock,  M.F.,  Assistant  Forester. 
Miss  Pauline  A.  Merchant,  Stenographer. 


Plant  Breeding. 


Donald  F.  Jones,  S.D.,  Geneticist'in  Charge. 
P.  C.  Mangelsdorf,  M.S.,  Assistant. 


Soil  Research. 


Tobacco  Sub-station 
at  Windsor. 


M.  F.  Morgan,  M.S.,  Investigator. 
C.  M.  Slagg,  M.S.,  in  Charge. 


The  Wilson  H.  Lbb  Co. 


The  European  Red  Mite  in  Connecticut 
Apple  Orchards. 

Paratetranychus  pilosus  Can.  &  Fanz. 
By  Philip  Garman,  Ph.D. 


Brown  foliage,  a  result  of  the  feeding  of  the  European  red  mite, 
was  first  noticed  on  apples  in  Connecticut  in  1920,  when  a  block 
of  Baldwins  in  a  large  commercial  orchard  near  Branford  became 
discolored.  Since  that  time  the  trouble  has  increased  rather  than 
decreased  in  the  State,  and  the  mite  now  seems  to  be  well  es- 
tablished, threatening  serious  damage  in  some  sections  every  year. 
What  can  be  done  to  bold  it  in  check  has  been  asked  from  time  to 
time,  and  we  are  now  able  to  offer  what  seems  to  be  a  practical 
remedy,  together  with  facts  about  habits  and  life  history  of  the 
mite  which  should  enable  the  orchardist  to  gain  control. 

History. 

The  European  red  mite  was  described  in  1876  from  Italy:  it 
has  been  noticed  in  several  countries  of  Europe  having  been  given 
considerable  attention  as  a  pest  in  Sweden.  In  America  it  has 
been  present  for  many  years,  but  has  been  confused  with  other 
species,  notably,  the  clover  mite  (Bryobia  pretiosa  Koch)  and  the 
common  red  spider  (Tetranychus  bimaculatus  Harvey)  from  both 
of  which  it  is  distinct.  On  the  Pacific  coast  it  has  passed  under 
the  name  of  citrus  mite  and  apparently  others,  and  has  done 
serious  damage  in  that  locality.  It  was  noted  in  Canada  in  1915,1 
by  Frost  in  Pennsylvania9  in  1919,  was  found  in  Connecticut  in 
1920,10  and  since  then  has  been  reported  from  Maryland,  New 
York  and  Ohio.  The  mite  was  recognized  as  present  in  California 
by  Essig4  in  1922,  though  it  has  probably  been  there  much  longer. 

Nature  of  the  Injury. 

A  heavy  infestation  of  red  mites  turns  leaves  of  apple  trees 
brown  early  in  June,  and  if  continued  gives  them  a  dead  appear- 
ance in  July.  This  results  in  undersized  and  poorly  colored  fruit 
and  affects  the  vitality  and  set  of  fruit  for  the  following  season. 
On  plums  and  apples,  a  little  later,  there  is  considerable  defoliation. 
A  moderate  infestation  leaves  the  trees  with  sickly  foliage  and 
prevents  growth  of  fruit  the  latter  part  of  the  summer,  a  condition 


104  CONNECTICUT  EXPERIMENT  STATION.  BULLETIN   252. 

often  unnoticed  by  the  orchardist,  but  very  conspicuous  as  com- 
pared with  trees  free  of  mites. 

Distribution. 

The  red  mite  is  present  in  Connecticut,  Massachusetts,  New 
Jersey,  New  York,  Maryland,12  Pennsylvania,  West  Virginia  and 
Ohio.  It  has  also  been  reported  from  Canada.  In  the  west, 
Oregon  and  California  consider  it  worthy  of  attention  and  it  will 
probably  be  found  in  many  other  localities  where  perhaps  it  is  not 
numerous  enough  at  present  to  invite  attention. 

In  Connecticut  it  is  well  distributed,  having  been  seen  in,  or 
received  from,  Fairfield,  Hartford,  Middlesex,  New  Haven  and 
New  London  Counties.  The  most  serious  damage  seems  to  have 
been  done  in  the  southern  part  of  the  State  and  little  complaint 
has  been  heard  from  the  more  northern  counties. 

Host  Plants. 

The  species  has  been  found  by  the  author  on  rose,  pear,  peach, 
plum,  cherry,  apple  and  elm.  It  is  reported  to  infest  prune  trees 
in  Pennsylvania,2  and  is  known  to  infest  almond,  prune  and  citrus 
fruits  in  California.3  Most  damage  is  done  to  apples  and  plums 
in  Connecticut,  though  occasionally  peach  trees  in  the  vicinity 
of  infested  apples  have  been  injured. 

Habits  and  Life  History. 

Examine  an  infested  tree  in  winter  after  the  leaves  have  fallen 
and  you  will  note  on  branches  the  size  of  a  lead  pencil  (sometimes 
on  those  as  much  as  two  inches  in  diameter)  a  coating  of  small 
red  eggs,  which  if  numerous  enough  will  not  require  magnification 
to  see  them.  They  are  dark  red  in  color  and  are  most  abundant 
around  bud  scars  and  in  crevices — resembling  a  coating  of  red 
brick  dust.  Wise  orchardists  know  the  signs  and  know  that 
trouble  may  be  in  store — and  act  accordingly.  These  are  the 
winter  eggs,  which  carry  the  pest  over  from  season  to  season. 
Watch  carefully  and  you  will  find  them  hatching  about  the  middle 
of  April  or  first  of  May;  or,  in  terms  of  the  development  of  the 
apple  tree,  at  the  time  when  the  blossom  buds  of  most  varieties 
begin  to  show  pink;  better  still  when  the  leaves  are  about  an  inch, 
long.  From  the  twigs  the  young  mites  make  their  way  to  the 
leaves  and  begin  to  feed,  completing  their  development  in  two 
weeks,  but  sometimes  requiring  longer  if  a  cold  spring  is  at  hand. 
By  the  first  of  June,  conditions  being  favorable,  they  begin  to 
multiply  rapidly,  passing  the  entire  cycle  in  three  weeks  or  snorter 
if  the  weather  is  warm.  The  life  period  is  such  that  an  overlapping 
of  broods  now  begins  for  the  following  reasons.  The  egg  develops 
in  6-13  days  or  an  average  of  nine  days,  and  the  mites  require 


THE  EUROPEAN  RED  MITE.  105 

about  as  long  to  complete  their  development,  or  long  enough  to 
begin  laying  eggs  (nine  days  more).  If  we  now  allow  15  days  as 
the  average  life  of  the  adult  during  which  time  the  eggs  are  laid, 
not  all  at  one  time  but  a  few  each  day,  then  at  the  end  of  15  days 
under  favorable  conditions  the  first  eggs  of  the  particular  female 
will  have  hatched  and  will  be  well  along  to  maturity,  giving  two 
different  generations  on  the  leaf  at  one  time.  This  apparently 
takes  place  shortly  after  the  first  of  June  in  Connecticut,  making 
it  impossible  to  apply  separate  sprays  for  different  broods  during 
the  summer.  In  all,  considering  the  length  of  the  cycle,  some  six 
generations  might  easily  occur  in  a  single  summer,  but  it  is  not 
always  safe  to  figure  natural  laws  or  processes  by  such  simple 
mathematics.  The  number  of  generations  in  this  case  is  of  minor 
importance,  but  our  experience  indicates  that  most  damage  is 
done  in  June  and  early  July  when  multiplication  is  most  rapid, 
and  before  enemies  become  numerous. 

The  female  is  not  a  great  egg  layer,  but  is  capable  of  laying  as 
many  as  34  eggs,  at  the  rate  of  one  or  two  per  day.  By  the  middle 
of  August,  many  eggs  are  laid  on  the  twigs  and  in  the  calyx  and 
stem  cavities  of  the  fruit,  and  by  September  15  the  winter  eggs 
are  being  laid  rapidly.  The  adults  die  shortly  after  and  show  no 
tendency  to  hibernate  in  this  climate. 

The  time  required  for  development  in  each  stage  is  shown  in 
the  following  tables : 

Table  1 — Length  op  Incubation  Period. 


Eggs  Laid 

Eggs  Hatched 

Period,  Days 

Mean  Temp.,  F 

May  16 

May  29 

13 

63.2 

May  18 

May  29 

11 

64.2 

May  21 

May  29 

8 

May  21 

June    1 

10 

67\2 

June  24 

June  30 

6 

June  24 

June  30 

6 

July   11 

July  17 

6 

73.  i 

Aug.    6 

Aug.  14 

8 

Aug.    8 

Aug.  16 

8 

Aug.    8 

Aug.  17 

9 

Aug.  29 

Sept.    6 

8 

Aug.  16 

Aug.  30 

14 

65.5 

Aug.  17 

Aug.  30 

13 

66.4 

Sept.    3 

Sept.    9 

6 

72.0 

Table 

2 — Period  from 

Egg  to  Adult 

Egg  Hatched 

Adult  Obtained 

Period,  Days 

Mean  Temp.,  F 

May  29 

June    5 

7 

66.6 

June     1 

June    8 

7 

June    9 

June  19 

10 

65*.  i 

June  10 

June  17 

7 

July   11 

July  16 

5 

77.  i 

July  25 

Aug.    1 

7 

72.9 

July  25 

Aug.    3 

9 

Aug.  30 

Sept.   9 

10 

Aug.  14 

Aug.  23 

9 

65 '.4 

106  CONNECTICUT  EXPERIMENT  STATION.  BULLETIN   252. 

Table  3 — Preoviposition  Period  of  Adult  Female. 

Female  Emerged  First  Egg  Laid              Period,  Days       Mean  Temp.,  F. 

June     7  June  10  3  61.0 

July     8  July     9  1  71.3 

July    16  July   19  3  79.2 

July    16  July   19  3  79.2 

Aug.     6  Aug.     8  2  

Aug.  10  Aug.  17  7  .71.8 

Sept.    9  Sept.  11  2 

Table  4 — -Length  of  Ltfe  of  Adults. 

Adult  Emerged  Adult  Died  Period,  Days      Mean  Temp.,  F. 

June  7  June  21  14  (female)  .... 

June  9  June  30  21  

July  8  July  22  14  (female)  79.0 

July  16  July  22                        6  (female)  82.2 

Aug.  10  Aug.  29  19  (female)  68.1 

Aug.  3  Aug.  17  14  (male)  74.8 

Aug.  6  Aug.  19  13  (female)  

Table  5 — Eggs  Laid  by  Adult  Females. 

First  Egg  Adult  Died  Total  Number 

June  10  June  21  18 

July     9  July  22  22 

June  10  June  21  16 

June    9  June  30  34 

Table  5a— Life  History  of  European  Red  MiTE.f 


Adult  Eggs  from    Total  Period, 

Laid  Hatched  Obtained  Adult  Days 

May  21  May  29  June  5  (male)      15 

May  21      June  7  June  10  20 

July  5                July   16  (male)                11 

July  7               July   16  July   19  12 

July  21               Aug.    3  (male)              13 

July  19  July  25  Aug.     1  (male)               13 

Aug.  6  Aug.  14  Aug.  23                          17 

Early  stages  feed  mostly  on  the  underside  of  the  leaf,  but  as  the 
leaf  becomes  crowded,  many  adults  move  to  the  upper  surface  and 
feed  there.  Very  little  web  is  spun  at  any  stage,  the  larvae  and 
nymphs  spinning  more  than  the  adults. 

Methods  of  Spread. 

Wind  is  the  most  important  agent  in  local  distribution  of  the  red 
mite.  Many  spin  down  from  the  leaves  on  short  threads  and  if  a 
strong  wind  is  blowing,  are  probably  carried  for  a  considerable 
distance.  Distribution  of  infested  nursery  stock  is  probably  re- 
sponsible for  spread  of  the  mite  since  the  eggs  are  small  and  easily 
overlooked.  Probably  many  are  carried  on  the  fruit,  especially 
winter  apples,  which  sometimes  contain  eggs  in  calyx  and  stem 
cavities. 


t  Continuous  records  of  single  individuals. 


the  european  red  mite.  107 

The  Different  Stages. 

The  European  red  mite  passes  through  the  following  stages: — 
egg:  active  larva — quiescent  larva:  active  first  nymph — quiescent 
first  nymph:  active  second  nymph — quiescent  second  nymph: 
adult  male  or  female.  During  quiescent  periods  the  mites  are  in- 
active and  no  food  is  taken.  The  male  usually  emerges  shortly 
before  the  female  and  awaits  the  emergence  of  the  latter.  Eggs 
are  laid  within  a  few  days  after  emergence  of  the  adult  female. 
There  is  no  difference  in  the  number  of  immature  stages  of  male 
and  female. 

Description. 

Adult  females  are  dark  velvety  red  in  color,  the  nymphal  stages 
and  the  male  dark  brown  or  green.  Winter  eggs  are  dull  red, 
summer  eggs  usually  brown. 

Egg — Slightly  flattened  above,  radially  grooved  and  with  a  short 
stalk  arising  from  the  center,  the  stalk  being  longer  than  the  vertical 
diameter  of  the  egg.     Transverse  diameter  of  egg  .15  mm. 

Larva — Nearly  orange  in  color  when  recently  hatched,  later 
turning  dark  green  or  brown;  mite  with  three  pairs  of  legs;  length 
.16-  18  mm. 

Protonymph — Very  dark  green  or  brown  in  color;  with  four  pairs 
of  legs,  the  latter  quite  pale;  length  .19-.25  mm. 

Deutonymph — Very  dark  green  or  brown;  legs  paler;  length 
.25-30  mm. 

Adult,  female — Color  dark  velvety  red  or  brown  with  conspic- 
uous white  dots  on  dorsum  at  base  of  setae;  26  setose  dorsal 
bristles  in  all;  tarsi  provided  with  a  single  claw  widest  at  the  mid 
point  and  with  apparently  five  (there  are  probably  six)  appendic- 
ulate  spurs  projecting  at  right  angles  (Fig.  2,  4) ;  four  tenent  hairs 
with  hooked  tips  arise  from  the  base  of  the  claw  and  exceed  it  con- 
siderably in  length;  collar  tracheae  consisting  of  a  single  tube 
(Fig.  2,  3)  dilated  at  tip  to  form  a  spherical  chamber;  maxillae 
consisting  of  four  segments,  the  last  tipped  with  a  short  spatulate 
body,  probably  representing  an  additional  segment;  next  to  the 
last  segment  with  a  strong  hook,  and  the  last  with  five  setae  (two 
apical,  two  basal  on  the  dorsum,  and  one  lateral)  and  a  clavate  hair 
between  the  two  dorsal  pairs;  length  of  adult,  .28-.31  mm. 

Male — Much  smaller  than  the  female,  the  tip  of  the  abdomen 
being  much  more  pointed  and  the  color  usually  brown,  never  red; 
genitalia  as  in  Fig.  2,  5,  length  .26-.28  mm. 

Difference  from  Other  Economic  Species. 

There  are  abundant  differences  between  the  European  red  mite 
and  the  common  red  spider,  Tetranychus  bimaculatus  Harvey. 
The  dorsal  setae  are  smaller  in  the  latter  species  and  the  collar 
tracheae  are  much  different,  being  hooked  and  segmented  (see  Fig. 


108 


CONNECTICUT   EXPERIMENT   STATION. 


BULLETIN   252. 


2,  8).     The  eggs  are  spherical,  usually  pale,  and  without  grooves 
or  stalk. 

Bryobia  pretiosa  Koch,f  the  clover  mite,  is  distinguishable  at 
sight,  being  considerably  natter  and  wrinkled  above  and  with  a 
number  of  flat  scalloped  plates  around  the  margin  of  the  body  of 
the  adult.  There  are  two  claws  on  each  tarsus  instead  of  one  and 
the  front  pair  of  legs  is  much  longer  than  any  of  the  others.  The 
eggs  are  red  but  are  larger,  usually  measuring  .19-.20  mm.  in 
diameter,  and  lack  the  radial  grooves  and  the  dorsal  stalk  present 
in  P.  pilosus. 


Figure  2.  Structures  of  European  red  mite,  Paraletranychus  pilosus  Can. 
and  Fanz.  and  common  red  spider,  Tetranychus  bimaculatus  Harvey. 

1,  Paraletranychus  pilosus,  seta  of  dorsum  846  times  enlarged;  2,  egg, 
14  times  enlarged;  3,  collar  tracheae  and  mandibular  plate,  714  times  enlarged; 
4,  tarsus  of  first  pair  of  legs  of  female,  921  times  enlarged;  5,  penis,  1400  times 
enlarged. 

6,  Tetranychus  bimaculatus,  seta  of  dorsum,  846  times  enlarged;  7,  egg, 
14  times  enlarged;  8,  collar  tracheae  and  mandibular  plate,  714  times  enlarged; 
9,  tarsus  of  first  pair  of  legs  of  female,  921  times  enlarged;  10,  penis,  1400 
times  enlarged. 


Number  of  Mites  Necessary  to  Produce  Browning. 

Some  varieties  of  apples  withstand  much  more  of  an  infestation 
without  showing  the  effects  than  others.  Spy  and  Wealthy  trees 
were  browned  in  1923  by  12  to  33  mites  per  leaf,  estimated  from  the 
number  of  cast  skins  found  after  browning  was  noticed.  Hurlbut 
trees  with  55  to  133  per  leaf  suffered  severe  browning. 

t  Bryobia  pratensis  Garman. 


the  european  red  mite.  109 

Varietal  Preferences. 

Greening  trees  rarely  have  as  many  mites  per  leaf  as  other  var- 
ieties, and  no  instances  have  been  observed  in  Connecticut  where 
severe  injury  has  been  done  to  this  variety.  Baldwin  is  perhaps 
the  most  commonly  injured,  but  Hurlbut.  York  Imperial,  Mc- 
intosh, Wealthy,  Northern  Spy  and  Fall  Pippin  have  been  in- 
jured, in  some  cases  severely.  Thin  leaved  varieties  are  most  sus- 
ceptible. 

Natural  Enemies. 

Some  of  the  most  puzzling  features  of  the  appearance  and  dis^- 
appearance  of  the  red  mite  are  connected  with  the  occurrence  of 
predaceous  enemies.  An  orchard  may,  for  instance,  be  heavily 
infested  one  season  and  show  almost  no  mites  the  following  year, 
although  no  spraying  has  been  done  in  the  meantime.  This  is 
often,  though  not  always  explained  by  the  presence  of  enemies 
which  in  Connecticut  seem  able  to  conauer  and  almost  eradicate 
the  mite  once  every  two  or  three  years.  Thus  in  1922,  a  heavy 
infestation  at  North  Branford  was  reduced  almost  to  the  zero 
point  and  no  outbreak  occurred  the  following  year.  In  1923, 
thrips,  coccinellids,  and  small  Hemiptera  such  as  Triphleps 
insidiosa  were  numerous  in  orchards,  and  greatly  checked  the 
mite  in  several  places. 

Three  species  of  thripsf  were  found,  a  small  bugj,  a  lady  beetle§, 
a  predaceous  mite ||,  and  a  small  undetermined  Neuropteron.  All 
of  these  destroyed  eggs  of  the  red  mite  with  relish,  one  thrips  being 
observed  to  eat  19  eggs  in  twenty-four  hours,  while  an  adult 
Stethorus  on  being  observed  took  six  eggs  and  three  mites  within 
five  minutes. 

Enemies  of  the  red  mite  are  most  numerous  in  July  and  August 
and  when  numerous  enough  keep  the  pest  in  check  in  spite  of  its 
rapid  multiplication  at  this  time  of  year.  One  or  two  thrips  per 
leaf  are  apparently  enough  to  keep  in  advance  of  an  infestation 
because  of  their  enormous  appetite  for  mite  eggs,  and  their  habit 
of  attacking  mites  themselves  when  eggs  are  scarce.  They  often 
leave  the  foliage  and  twigs  with  empty  transparent  egg  shells, 
having  sucked  out  their  contents  and  departed. 

Weather  Conditions  Affecting  Abundance. 

Adverse  weather  conditions  are  responsible  for  subsidence  of 
outbreaks  in  some  cases,  but  it  is  sometimes  difficult  to  say  whether 
tnis  or  the  abundance  of  enemies  is  the  cause.  Conditions  favor- 
able to  the  mite  may  be  favorable  to  development  of  the  enemies  or 
vice-versa.  It  has  been  reported  that  bad  outbreaks  have  followed 
a  very  severe  winter  and  the  great  numbers  of  mites  in  1920  and 

t  Leptothrips  mali  Fitch,  Scolothrips  6-maculatus  Pergande  and   H aplo thrips  sp.;  deter- 
mined by  Dr.  A.  C.  Morgan. 
t  Triphleps  insidiosa  Say. 
§  Stethorus  punolum  Leconte. 
II  Seius  pomi  Parrott. 


110  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   252. 

1923  certainly  followed  abundan'  snows  and  cold  weather.  How- 
ever, a  serious  outbreak  occurred  in  1922  after  a  rati  er  mild  winter, 
and  the  infestations  in  1923  did  not  become  serious  until  mid- 
summer, whereas  if  cold  weather  had  much  effect  this  should  have 
begun  more  promptly.  Heavy  rainfall  or  better  a  series  of 
showers  at  frequent  intervals  in  summer  is  successful  in  keeping 
an  infestation  from  gaining  headway,  as  witnessed  in  this  State  in 
1922.  This  is  due  to  the  fact  that  many  mites  are  washed  from  the 
leaves  and  are  unable  to  regain  the  tree.  It  is  quite  possible  that  a 
rainy  period  in  September  would  decidedly  affect  the  abundance 
of  the  mite  the  following  season,  though  no  cases  of  this  sort  have 
been  observed.  In  1923,  the  prolonged  dry  period  from  the  middle 
of  June  to  September  favored  development  and  several  orchards 
were  damaged  severely. 

Control  Measures. 

Owing  to  the  uncertainty  that  weather  and  enemies  will  produce 
a  balance  in  favor  of  the  orchardist,  treatments  for  control  must  be 
considered  and  a  regular  schedule  adopted.  There  are  periods 
when  the  mite  is  especially  vulnerable  and  a  thorough  spray  is  of 
much  value;  and  it  is  a  good  policy  to  learn  to  know  the  mite  in  its 
different  stages  so  that  damage  may  be  anticipated  and  prevented. 
As  with  many  insects  the  best  time  to  concentrate  efforts  is  in  early 
spring  and  sprays  at  this  time  should  go  far  towards  a  control  for 
the  entire  season,  especially  in  this  climate.  It  is  well,  therefore, 
to  keep  a  sharp  lookout  for  winter  eggs  when  the  annual  pruning 
is  done  and  not  to  wait  until  the  leaves  turn  brown  before  con- 
sidering treatment. 

Sprays  for  the  Winter  Eggs. 

The  first  attack  should  be  on  the  overwintering  eggs  which  may 
be  reached  with  sprays  and  largely  destroyed.  Laboratory  tests 
were  conducted  in  1920-21  with  a  view  to  finding  the  most  effective 
treatments  for  this  purpose.  Some  of  the  tables  are  given  below 
together  with  tests  of  several  other  compounds  reaching  us  since 
these  were  made. 

In  the  tables,  the  names  of  a  number  of  proprietary  compounds 
appear,  and  the  following  explanation  in  regard  to  their  general 
composition  and  source  is  necessary.  Such  compounds  as  lime- 
sulphur,  and  Scalecide  are  too  well  known  to  need  comment. 

"Jarvis  Compound." —  A  miscible  oil  containing  phenol;  manu- 
facturer J.  T.  Robertson;  obtained  from  Apothecaries  Hall  Co., 
Waterbury,  Conn. 

"  Kero-spray." — A  commercial  kerosene  emulsion ;  manufacturer, 
Kero-Spray  Co.,  198  9th  St.,  Jersey  City,  N.  J. 

" Keresol." — An  oil  spray  containing  70  per  cent,  kerosene; 
obtained  from  Mr.  A.  A.  Claasen,  Mascher  and  Turner  Streets, 
Philadelphia,  Pa. ;  effect  of  spray  on  trees  unknown. 


THE    EUROPEAN   RED   MITE. 


Ill 


"Sulco  V.  B." — A  spray  containing  fish-oil  and  small  per  cent, 
phenol;  manufactured  by  Cook  &  Swan  Co.,  148  Front  St.,  New 
York;  obtained  from  Apothecaries  Hall  Co.,  Waterbury;  effect 
on  apple  trees  unknown,  probably  safe. 

"Wormol." — A  miscible  oil  recommended  for  use  against  peach 
borers  by  the  General  Chemical  Company;  obtained  from  General 
Chemical  Company,  25  Broad  St.,  New  York,  N.  Y. ;  effect  upon 
apple  trees  unknown. 

"B.  T.  S." — Barium  tetrasulphide,  a  lime-sulphur  substitute;  a 
General  Chemical  Company  product. 

"Sunoco  Spraying  Oil". — A  miscible  mineral  oil;  apparently  safe 
on  apple  trees;  sold  by  Sun  Oil  Company,  Philadelphia,  Pa. 

"Target  Brand  Scale  Destroyer" — A  miscible  oil  containing 
phenol;  sample  submitted  by  the  Interstate  Chemical  Company, 
Jersey  City,  N.  J. 

Tables  Showing  Results  op  Treating  Eggs  of  European  Red  Mite 
With  Different  Insecticides. 


Table  6. 

Exp. 

Total  Number 

Number 

Per  Cent. 

Date 

Date 

No. 

Treatment            of  Eggs  Used 

Hatched 

Hatched 

Treated 

Examined 

1. 

Kerosene  emulsion 

(10  per  cent,  kerosene) 

660 

402 

60.9 

Mar.  16 

Apr.   29 

2. 

Kero-spray 

1  part-25  parts  water 

298 

166 

56.0 

a 

a 

3. 

Sulco  V.  B. 

1  part-25  parts  water 

502 

255 

50.7 

a 

a 

4. 

Keresol 

' 

1  part-18  parts  water 

442 

265 

59.9 

u 

a 

5. 

Jarvis  Compound 

1  part-15  parts  water 

104 

6 

5.7 

a 

u 

6. 

Scalecide 

1  part-15  parts  water 

237 

22 

9.2 

« 

a 

7. 

Lime-sulphur 

1  part-9  parts  water 

652    ■ 

253 

38.8 

« 

a 

8. 

Dry  lime-sulphur 

12  lbs.-50  gals,  water 

418 

125 

29.9 

a 

a 

9. 

B.  T.  S. 

12  lbs.-50  gals,  water 

349 

162 

46.4 

a 

a 

10. 

Scalecide 

1  part-25  parts  water 

341 

115 

33.7 

u 

u 

11. 

Check 

no  treatment 

265 

151 

56.9 

— ■ 

u 

12. 

Scalecide 

1  part-15  parts  water 

150 

8 

5.3 

April.  7 

Apr.   29 

13. 

Scalecide 

1  part-15  parts  water 

669 

9 

1.3 

« 

a 

14. 

Scalecide 

1  part-35  parts  water 

838 

53 

6.3 

a 

a 

15. 

Scalecide 

1  part-25  parts  water 

744 

68 

9.1 

a 

a 

16. 

Scalecide 

1  part-50  parts  water 

462 

47 

10.1 

a 

« 

17. 

Check 

no  treatment 

253 

164 

65.0 

— 

a 

18. 

Check 

no  treatment 

100 

45 

45.0 

— 

u 

112 


CONNECTICUT   EXPERIMENT   STATION. 


BULLETIN    252. 


Table  7. 

Exp. 

T 

otal  Number 

Number 

Per  Cent. 

Date 

Date 

No. 

Treatment                < 

Lime-sulphur  1-9 

)f  Eggs  Used 

Hatched 

Hatched 

Treated 

Examined 

1." 

Nic.  Sulphate  1-500 

649 

189 

29.1 

Dec.  29 

Feb.  23 

2. 

((            ft                « 

Lime-sulphur 

2,166 

544 

25.1 

Feb.     8 

Mar.    2 

3. 

1  part-9  parts  water 

403 

45 

11.1 

Apr.     5 

Apr.   15 

4. 

«          <(          «( 

378 

18 

4.7 

Mar.  12 

Mar.  28 

5. 

ft           <(          « 

773 

268 

34.6 

Dec.  29 

.  Feb.  23 

Lime-sulphur  1-9 

6. 

Nic.  Sulphate  1-500 

165 

80 

48.4 

Apr.   13 

Apr.  28 

7. 

«           «           « 
Lime-sulphur 

221 

54 

24.4 

Apr.  13 

Apr.  29 

8. 

1  part-9  parts  water 

526 

351 

66:7 

Dec.  29 

Apr.  28 

9. 

ft           «           ft 

652 

253 

38.8 

Mar.  16 

Apr.  29 

10. 

«           »           » 

449 

132 

29.4 

Feb.  17 

May    3 

11. 

«           »           « 

299 

83 

27.7 

Mar.  10 

May    2 

Notes. 

Table  6.  Eggs  in  tests  1-11  were  taken  from  the  same  branch.  Those  in 
12-18  were  from  another  branch.  All  eggs  dipped  in  the  different  solutions, 
not  sprayed. 

Table  7.  Nos.  1-5  were  kept  indoors  after  treatment;  6-11  outdoors. 
Nos.  5  and  6  were  sprayed,  other  dipped. 


Table  8. 

Dry  lime-sulphur 

1. 

Y2  oz.-l  pint  water 

302 

114 

37.7 

Apr. 

5 

Apr.   15 

2. 

»           »         ft 

274 

6 

2.1 

Mar. 

12 

Mar.  28 

3. 

«           »         ft 

197 

74 

37.5 

Mar. 

4 

Mar.  25 

4. 

<(           »         «( 

418 

125 

29.9 

Mar. 

16 

Apr.  29 

Table  9. 

B.  T.  S. 

1. 

Y2  oz.-l  pint  water 

1,047 

368 

35.2 

Feb. 

8 

Mar.    2 

2. 

«(           «         « 

374 

124 

33.2 

Apr. 

5 

Apr.  15 

3. 

ft           «         it 

438 

35 

7.9 

Mar. 

12 

Mar.  28 

4. 

<(           »         ft 

234 

34 

14.5 

Mar. 

4 

Mar.  25 

5. 

Y2  oz.-l  pint  water 
B.  T.  S.  Y2  oz.-l  pt. 

349 
water 

162 

46.4 

Mar. 

16 

Apr.  29 

6. 

N.S.  1  part-500  part  water  282 

126 

44.6 

Apr. 

5 

Apr    29 

Table  10. 

1. 

Scalecide  l-15f 

773 

27 

3.5 

Dec. 

29 

Feb.  23 

2. 

1-15 

1,078 

0 

0.0 

Feb. 

8 

Mar.    2 

3. 

1-15    ■ 

412 

0 

0.0 

Apr. 

5 

Apr.   15 

4. 

"         1-15 

67 

0 

0.0 

Mar. 

12 

Mar.  28 

5. 

1-25 

173 

0 

0.0 

Mar. 

16 

Apr.     4 

6. 

1-50 

356 

11 

3.0 

Mar. 

16 

Apr.     4 

7. 

1-15 

119 

0 

0.0 

Mar. 

4 

Mar.  25 

8. 

1-15 

409 

135 

33.0 

Dec. 

29 

Apr.  28 

9. 

1-15 

104 

6 

5.7 

Mar. 

8 

Apr.  29 

t  Proportions  of  Scalecide  to  water. 


THE    EUROPEAN    RED   MITE. 


113 


Table  10 — Continued. 


Exp. 

Total  Number  Number 

Per  Cent. 

Date 

Date 

No. 

Treatment 

of  Eggs  Used    Hatched 

Hatched 

Treated 

Examined 

10. 

Scalecide  1-25 

341         115 

33.7 

Mar.    9 

Apr.  29 

11. 

1-50 

150            8 

5.3 

Apr.     7 

Apr.  29 

12. 

1-15 

669            9 

1.3 

Apr.     7 

Apr.  29 

13. 

1-25 

744          68 

9.1 

Apr.     7 

Apr.  29 

14. 

1-35 

838          53 

6.3 

Apr.     7 

Apr.  29 

15. 

1-50 

462          47 

10.1 

Apr.     7 

Apr.  29 

16. 

1-15 

326           55 

16.8 

Feb.  17 

May    3 

Notes. 
Table  8.     Nos.  1-3  kept  indoors.  4  outdoors. 
Table  9.     Nos.  1-4  kept  indoors,  5  and  6  outdoors. 

Table  10.  Tests  1-7  were  kept  indoors  after  treatment;  8-16  were  kept 
outdoors.  Numbers  10-15  were  sprayed,  others  were  dipped  in  spray  solu- 
tions. 

Table  11. 


Exp. 

No. 

1. 
2. 
3. 

4. 
5. 
6. 

7. 


10. 

11. 
12. 
13. 


Total  No. 

of  Eggs 

Used 

233 
262 
180 
325 


Treatment 
Sunoco  spraying  oil  1-15 
Sunoco  spraying  oil  1-15 
Sunoco  spraying  oil  1-25 
Sunoco  spraying  oil  1-50 

Lime-sulphur,  1-6 297 

Lime-sulphur,  1-9 .224 

Target  brand   scale   de- 
stroyer, 1-15 357 

Target  brand  scale  de- 
stroyer, 1-50 265 

Red  engine  oil  1%  emul- 
sion with  fish  oil  soap. .     299 
Red  engine  oil  2%  emul- 
sion with  fish  oil  soap. .     322 

Scalecide  1-15 252 

Check,  no  treatment..  .  .     200 
Check,  no  treatment.. .  .     175 


No. 
Hatched 

4 
1 

6 
56 
68 

77 


37 


143 
136 


Per  Cent. 
Hatched 

1.7 

.4 

3.3 


14, 

22, 
29, 


13.9 
.0 


1 

71 

77 


Date 
Treated 

Feb.  1 
Mar.  15 
Mar.  15 
Feb.  3 
Feb.  3 
Feb.     3 

Feb.     3 

Feb.     3 

Mar.  15 

Mar.  15 
Mar.  15 


Date 
Examined 

Mar.  8 
Apr.  15 
Apr.  15 
Mar.    8 

Mar.  8 
Mar.    8 

Mar.    8 

Mar.    8 

Apr.  15 

Apr.  15 
Apr.  15 
Mar.  8 
Apr.   15 


14. 

Lime-sulphur  1-8.  . . 

666  - 

148 

22 

2        Apr. 

11 

May  15 

15. 

Scalecide  1-15 

644 

2 

2 

.3        Apr. 
.3        Apr. 

11 
11 

May  15 
May  15 

16. 

Sunoco  spraying  oil  1-15     573 

17. 

Red  engine  oil  2%  emul- 

sion with  fish  oil  soap. .     646 

31 

4 

8        Apr. 

11 

May  15 

18. 

Check,  no  treatment 

. . .     361 

127 

35 

1        

May  15 

Table  12 

(checks). 

Exp. 

Total  Number 

Number 

Per  CeDt. 

Date 

Date 

No. 

of  Eggs  Used 

Hatched 

Hatched 

Obtained 

Examined 

1. 

1,956 

345 

17.6 

Dec.  29 

Feb.  23 

2. 

527 

263 

49.9 

Feb.     9 

Mar.    4 

3. 

60 

45 

75.0 

Feb.  10 

Mar.    4 

4. 

2,421 

1,477 

61.0 

Feb.     8 

Feb.  23 

5. 

334      , 

326 

97.6 

Apr.     5 

Apr.  15 

6. 

359 

324 

90.2 

Apr.     8 

Apr.  28 

7. 

208 

185 

88.9 

Mar.    4 

Mar.  25 

8. 

402 

223 

55.4 

Mar.  10 

Mar.  28 

9. 

403 

333 

82.6 

Mar.  11 

Mar.  28 

10. 

430 

342 

79.7 

Mar.  12 

Mar.  28 

11. 

255 

209 

81.9 



Apr.     4 

114 

CONNECTICUT 

EXPERIMENT   STATION 

BULLETIN   252. 

Table  12  (checks) — Continued. 

Exp. 

Total  Number 

Number 

Per  Cent. 

Date 

Date 

No. 

of  Eggs  Used 

Hatched 

Hatched 

Obtained 

Examined 

12. 

421 

181 

42.9 

Dec.  29 

Apr.  28 

13. 

265 

151 

56.9 

Mar.  16 

Apr.  29 

14. 

253 

164 

64.8 

Apr.     7 

Apr.  29 

15. 

100 

45 

45.0 

Apr.     7 

Apr.  29 

16. 

162 

109 

67.3 

Apr.  13 

Apr.  28 

17. 

120 

20 

16.6 

Apr.     4 

Apr.  28 

18. 

155 

85 

54.8 

Apr.     5 

Apr.  29 

19. 

531 

337 

63.4 

Feb.  17 

May    3 

20. 

188 

114 

60.6 

Mar.  10 

May    2 

COMPA 

bative   Mortality 

of  Treated   Eggs 

OF 

European 

Red   Mite, 

Kept  Outdoors  and  Indoors  After  Treatment. 
Table  13. 

Hatched     Possible  Kill  Number  of 

Treatment                                      Per  Cent.       Per  Cent.  Eggs  Used 

61.0              0  7,355 

Check,  no  treatment 

54.9              0  2,195 


Jarvis  Compound. 


100 
89.1 


792 
104 


Indoors 
Outdoors 


Kero-spray 

86.5 

55.7 

0 
0 

445 
298 

Indoors 
Outdoors 

Sulco  V.  B 

49.9 
48.0 

18.6 
12.5 

879 
958 

Indoors 
Outdoors 

34.2 
59.9 

44.0 
0 

385 
442 

Indoors 
Outdoors 

Linseed  oil  emulsion 

56.0 
26.1 

8.4 
52.5 

841 
352 

Indoors 

Outdoors 

B.  T.  S 

26.7 
45.6 

56.3 
16.8 

2,093 
631 

Indoors 
Outdoors 

Lime-sulphur;  liquid  1-9 

22.1 
43.1 

63.8 
21.4 

3,596 
2,515 

Indoors 
Outdoors 

Lime-sulphur;  dry 

25.0 
29.9 

59.0 
45.5 

773 
418 

Indoors 
Outdoors 

Kerosene  emulsion 

31.6 
60.9 

48.2 
0 

227 
660 

Indoors 

Outdoors 

Wormol,  1  part  in  15  parts  water 

5.4 
14.7 

91.1 

73.2 

419 
292 

Indoors 
Outdoors 

Scalecide 

1.2 

9.9 

98.1 

81.8 

2,978 
4,043 

Indoors 
Outdoors 

Indoors 
Outdoors 


PLATE  V. 


1.  Quiescent  nymph  of  European  red  mite,  enlarged  80  times.  2.  Larvae 
of  predaceous  enemy  (Stethorus  punctum  LeConte).  3.  Pupa  and  adult  of 
same,  enlarged  10  times.  4  and  5.  Adult  females  of  European  red  mite, 
enlarged  13  times.     6.     Adult  female,  enlarged  80  times. 


EUROPEAN  RED   MITE. 


PLATE  VI. 


a.     Apple  leaves,  showing  leaf  injured  by  European  red  mite  (above), 
uninjured  (below). 


b.     Peach  leaves,  showing  leaf  injured  by  European  red  mite  (below), 
uninjured  (above). 

EUROPEAN   RED  MITE. 


PLATE  VII. 


a.      Infested  apple  tree  which  has  lost  much  foliage  from  the  attacks  of 

the  mite. 


b.     Eggs  on  calyx  end  of  apple,  and  on  twig,  three  times  enlarged;    insert, 
same  from  twig,  enlarged  about  ten  times. 

EUROPEAN  RED  MITE. 


PLATE  VIII. 


a.     View  in  orchard  of  Smith  T.  Bradley,  North  Braiif  ord,  showing  untreated 
trees  partially  defoliated  by  mite. 


b.     View  in  same  orchard  showing  trees  which  were  sprayed  with  linseed 

oil  emulsion. 

EUROPEAN   RED  MITE. 


THE   EUROPEAN   RED   MITE.  115 

Notes. 

Table  12.  Eggs  listed  here  were  not  treated  with  any  insecticide.  Numbers 
1-11  were  kept  indoors  in  moist  jars;   12-20  outdoors. 

Table  13.  The  percentages  in  the  column  headed  "possible  kill"  were 
obtained  by  comparing  each  with  the  check  hatch,  obtaining  the  actual  hatch, 
and  subtracting  this  number  from  100,  thereby  obtaining  the  per  cent,  killed. 
Where  the  per  cent,  hatched  is  higher  than  the  check  it  is  obvious  that  the 
insecticide  has  no  killing  power. 

Summary  of  Various  Treatments. 
Table  14. 

Exp.  Hatched  Possible  Kill        Number  of 

No.  Treatment  Per  Cent.  Per  Cent.  Eggs  Used 

1.  Check,  no  treatment 55.2                  0  9,550 

2.  Kero-spray 74.1                  0  743 

3.  SulcoV.  B 49.2  10.9  1,837 

4.  Keresol 47.9  13.3  827 

5.  Linseed  oil  emulsion 46.3  16.2  1,193 

6.  B.  T.  S 31.1  43.7  2,724 

7.  Lime-sulphur  (liquid) 30.8  44.3  6,111 

8.  Lime-sulphur   (dry) 26.3  52.4  1,191 

9.  Kerosene  emulsion 12 . 9  76 . 7  887 

10.  Wormol 9.2  83.4  711 

11.  Scalecide 7.6  86.2  7,021 

12.  2%  Red  engine  oil  emulsion.  . .  4.8  91.3  646 

13.  Jarvis  compound .6  99.0  896 

14.  Sunoco  spraying  oil .3  99.5  573 

Different  authorities  have  claimed  that  dormant  or  delayed 
dormant  sprays  of  lime-sulphur  either  killed  the  mites  before 
hatching,  prevented  them  from  reaching  the  leaves,  or  killed 
them  by  continued  action  after  reaching  the  leaves.  Although 
lime-sulphur  will  kill  some  of  the  eggs  as  shown  in  the  tables,  it 
has  been  our  experience  (see  Table  15)  that  it  does  not  prevent 
them  from  reaching  the  leaves  or  kill  them  off  in  appreciable 
numbers  after  they  begin  to  feed.  It  is  in  fact  a  much  less  efficient 
ovicide  for  the  red  mite  than  miscible  oils.  A  fairly  convincing 
example  of  this  is  found  in  the  table  below;  which  gives  the  results 
of  a  test  conducted  at  the  Experiment  Station  Farm  in  1923. 

Table  15 — Effect  of  Field  Treatments  on  the  Winter  Egg. 

Number  of  Fruit  Number  with  Live  Per  Cent. 

Treatment  Spurs  Examined  Mites  on  Leaves  Infested 

Scalecide  1-15 978  56  5.7 

Lime-sulphur  1-9 975  972  99. 6 

Check,  no  treatment 1,000  1,000  100.0 

Examination  of  the  trees  during  the  winter  indicated  a  nearly 
equal  infestation  of  all  blocks.  Sprays  were  applied  at  the  latest 
possible  date  considering  the  development  of  the  trees.  Nearly  a 
thousand  fruit  spurs  in  each  block  of  about  20  trees  were  ex- 
amined, every  twig  included  having  eggs  on  it  or  at  its  base.    It 


116  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   252. 

will  be  seen  that  lime-sulphur  checked  their  development  little  or 
none,  while  the  miscible  oil  used  was  considerably  more  effective. 

This  condition  continued  well  into  the  summer  and  trees  re- 
ceiving lime-sulphur  alone  as  a  delayed  dormant  spray  were  in 
practically  the  same  condition  as  those  receiving  no  spray,  that  is, 
in  the  amount  of  infestation  on  the  leaves.  What  virtue  there  is 
in  lime-sulphur  seems  to  rest  mainly  with  early  summer  sprays 
and  not  so  much  with  the  delayed  dormant.  Early  summer 
sprays  at  1.5-50  or  1-50  have  been  successful  in  three  different 
experimental  orchards  in  keeping  the  mite  in  control — and  this 
without  any  dormant  or  delayed  dormant  spray  whatsoever.  This, 
together  with  the  information  in  Table  15,  indicates  that  lime- 
sulphur  dormant  or  delayed  dormant  sprays  are  of  little  value  in 
red  mite  control. 

It  will  be  noted  in  Tables  7,  9  and  10  that  there  is  a  general  re- 
duction in  percentage  of  hatch  after  treatments  as  the  season 
advances  from  December  to  April  or  May.  This  is  probably  due 
to  embryonic  development,  but  the  membranes  do  not  split  as 
in  the  case  of  aphids.  The  outer  membrane,  however,  does  loosen 
up  and  may  be  peeled  off  with  a  needle  several  days  before  the 
mite  hatches.  These  facts  were  corroborated  in  practical  experi- 
ence at  the  Conyers  Farm  orchard  at  Greenwich,  in  charge  of 
Mr.  G.  A.  Drew.  Fall  spraying  in  this  orchard  with  miscible  oil 
killed  a  very  small  per  cent.,  while  spring  applications  were  quite 
effective. 

Scalecide  is  the  only  miscible  oil  which  has  been  given  a  field 
test,  and  it  is  shown  to  be  effective.  There  are  other  oil  emulsions, 
however,  which  should  do  the  work,  and  some,  notably  the  home- 
made lubricating  oil  emulsions,  apparently  are  causing  no  damage.8 
There  is  an  element  of  danger  in  using  them,  and  it  is  well  to 
observe  some  precautions  in  applying. 

1.  Make  sure  that  all  of  the  oil  emulsifies,  leaving  none  floating 
on  the  surface  of  the  water  in  the  spray  tank.  This  condition  will 
often  follow  the  use  of  old  material  which  has  been  on  hand  for 
a  year  or  more.    In  most  cases  it  is  best  to  have  fresh  stock. 

2.  Do  not  drench  the  trees;  spray  lightly,  covering  the  outer 
twigs  and  smaller  branches. 

3.  Do  not  spray  in  weather  so  cold  that  the  spray  freezes. 

4.  Apply  before  the  buds  break;  as  a  late  dormant  spray. 
This  usually  falls  several  weeks  before  the  delayed  dormant  spray. 

5.  Do  not  use  at  all  unless  red  mite  eggs  are  very  numerous, 
or  unless  you  expect  a  serious  outbreak;  an  application  of  miscible 
oil  once  every  three  years  should  be  sufficient  when  the  mite  is 
once  in  control. 

Summer  Sprays. 

Different  substances  have  been  tested  on  the  mites  themselves 
for  killing  power,  and  the  results  are  given  below  in  Table  16. 
Such  tests  are  not  so  satisfactory  as  similar  tests  for  the  eggs,  be- 


THE   EUEOPEAN   RED    MITE. 


117 


cause  of  the  fact  that  the  mite  is  susceptible  to  changes  in  tem- 
perature and  also  to  condition  of  the  food  plant.  At  any  rate, 
there  is  considerable  more  variation  in  the  results  obtained, 
though  they  indicate  in  a  general  way  the  effectiveness  of  soaps, 
lime-sulphur  solutions,  and  oil  emulsions. 


Table  16 — Results  of  Laboratory  Tests  to  Control  Mites. 

Exp.  Insecticide  No.  No.     Per  Cent.     Temp,  of  Air 

No.  Used  Dead       Alive        Dead  F  Dates 

1 .  Ivory  soap  flakes  2  lbs. 

—50  gals 67         12        84.8  May  20-22 

2.  Ivory  soap  2  lbs. — 50 

gals,  plus  Melrosine 

1  part  to  100 71         14        83.5  May  20-22 

3.  Ivory  soap  flakes  2  lbs. 

—50  gals 409  2        99.5        73  May  13-18 

4.  Ivory  soap  flakes  2  lbs. 

—50  gals 406  4  99.0  80.5-82  May  13-18 

5.  Lux  2  lbs. —50  gals...  107  1  99.0  73  May  13-18 

6.  Lux  2  lbs.— 50  gals...  164  3  98.1  80.5-82  May  13-18 

7.  Potash  fish  oil  soap  10 

lbs.— 50  gals 12        14        46 . 1  May  23-25 

8.  Fish  oil  soap  5  lbs. — 

50  gals 13.       41        24.0  May  23-25 

9.  Fish  oil  soap  10  lbs. — 

50;    sulphur  16  lbs. 

50  gals 16        93         14.6        80.5-82        May  27-31 

10.  Borax  soap  4  lbs. — 48 

gals,  water 128        26        83 . 1         60-79  Aug.  17-18 

11.  Linseed  oil  emulsion  1 

part— 20  parts  water      81  5         94.1         70-74  Aug.  17-18 

12.  40%  nicotine  sulphate 

Mpt.— 50  gals 114  5        95.7  July  28-30 

13.  Borax  soap  6  lbs. — 50 

gals 141  6        95.9  July  28-30 

14.  Fels  naphtha   soap   4 

lbs.— 50  gals 15  0       100  July  28-29 

15.  Star  soap  4  lbs. — 50 

gals 23  2  92  July  29-30 

16.  Dusted  with  sulphur..  22  59  27.1  73                   May  12-18 

17.  Dusted  with  sulphur..  101  2  98.0  80.5-82        May  12-18 

18.  Lime-sulphur     1 — 40 

nicotine   sulphate    1 
—500 36  2        95.0        60-79  Aug.  15-16 

19.  Lime-sulphur     1—40; 

nicotine   sulphate    1 

—500 141         18        88.7        60-79  Aug.  17-18 

20.  Ace-Hy  1—400  f 108      254        29.8  June  31-July  1 

21.  Ace-Hy  l—200t 40  2        95.2  Aug.  29 

22.  Lime-sulphur  1 — 43  }/i 

gals 79  28  73.8  July  28-30 

23.  Check,  no  treatment..  4  53  9.5  73                  May  12-18 

24.  Check,  no  treatment..  22  31  41.7  80.5-82         May  12-18 

25.  Check,  no  treatment..  12  70  14.6  May  20-22 

26.  Check,  no  treatment..  2  84  2.3  60-79            Aug.  17-18 


t  An  insecticide  no  longer   on  the  market;    containing   cyanide    (CN)    as   the   active 
ingredient. 


118 


CONNECTICUT   EXPERIMENT   STATION. 


BULLETIN   252. 


Sulphur  dusts  are  variable,  both  in  laboratory  and  in  the  field, 
but  at  least  one  factor  influencing  their  effectiveness  is  found  in 
the  temperature  of  the  atmosphere  as  shown  in  the  two  following 
charts,  giving  the  killing  power  of  sulphur  dust  and  a  dust  con- 
taining 88  per  cent,  sulphur  and  10  per  cent,  lead  arsenate. 

"Pomodusf't  is  now  on  the  market  and  was  apparently  effective 
in  controlling  the  red  mite  under  the  weather  conditions  experi- 
enced in  1923.     The  totally  different  action  of  sulphur  dusts  in 


_     --^^ 

80 
70 

Q 

-J 

40 
X     J 

&    J 

' 

, —                             ^y 

/ 

^^ 

/  / 

' 

#  y 

s 

/ 

rjhec^ 

' 

7 

0                                      7 

5                           a 

o                           a 

5                                  90 

TEMPERATURE.  °F 

Chart  1.     Showing  kill  obtained  with  sulphur  dust  and  "Pomodust"  at 
different  temperatures;  exposure  in  each  case  24  hours. 


1922  may  be  explained  by  the  lack  of  excessive  heat,  and  the  dry 
weather  which  doubtless  influenced  the  results  in  1923. 

Field  tests  have  been  conducted  in  five  different  orchards  in 
Connecticut.  The  first  were  carried  out  at  the  Plant  Brothers 
orchard  in  Branford  in  1920.  Soap,  soap  and  nicotine  sulphate, 
and  sulphur-arsenate-nicotine  dust  were  tried,  but  results  were 
inconclusive  due  to  the  lateness  of  the  applications.  In  1921,  no 
field  tests  were  conducted  but  in  1922  serious  outbreaks  occurred 
and  experiments  were  undertaken  in  three  different  orchards. 
Good  control  was  secured  with  linseed  oil  emulsion,  soaps,  and  a 
lime-sulphur-lead-arsenate-nicotine  mixture.  Tests  at  the  Bradley 
orchard  showed  good  control  with  linseed  oil  emulsion  and  with 
fish  oil  soap.  Good  control,  however,  was  obtained  with  borax 
soap  and  lime-sulphur-lead-arsenate-nicotine  combination  in  the 


t  Chemical  analysis  by  the  Connecticut  Station,  Department  of  Chemistry,  showed  that 
it  contains  sulphur  87.79  per  cent.,  lead  arsenate  9.80  per  cent.,  and  a  trace  of  iron;  water 
soluble  arsenic  .24  per  cent. 


THE   EUROPEAN   RED    MITE. 


119 


Milford  orchard  of  F.  N.  Piatt.  Counts  were  not  made  in  the 
Milford  orchard,  but  from  a  practical  standpoint  results  were 
good,  since  the  foliage  continued  green  throughout  the  summer. 


90 
30 

gO^-^" 

Q70 

y 

z 

•J 

/ 

y 

Udn 

f  f      

Q: 
10 

* 

a2^-^ 

y 

/ 

4-  8  /<5  24 

hours  exposure: 

Chart  2.     Showing  kill  obtained  with  "Pomodust"  at  different  tempera- 
tures and  different  lengths  of  exposure. 

Table  17 — Results  of  Field  Tests  with  Soaps,  Linseed  Oil  Emulsion 

and  Self-Boiled  Lime-Sulphur 

In  Bbadlet  Orchard. 

No.  of  No.  of  Date  of 
Leaves  Twigs  Date  of  Exam- 
Insecticide               No.           No.       Per  Cent.    Exam-  Exam-  Treat-  ination 
Used                   Alive       Dead          Dead          ined  ined  ment  1922 

Linseed  Oil  1  gal.f 

Ivory  soap  13^  lbs. 

Water  100  gals...    718      1,524        67.9        80        10        June  2        June  6 

Ivory  soap  6  lbs. 

Water  200  gals...  1,743         779        30.8        60  9        June  2        June  6 

"Kerospray"  1  gal. 
—100  gals 916         381        29.5        50  6        June  2        June  6 

Fish  oil  soap   14 
lbs.— 200  gals . .    691         655        48.6        54  6        June  2        June  7 

Self-boiled  lime- 
sulphur  (8-8-50) 

Kayso  2^  lbs. — 
200  gals 951         356        27.2        64  8        June  2        June  8 

None 1,592         278        14.  65  7        June  8 

t  Prepared  according  to  directions  in  Mass.  Agr.  Exp.  Sta.  Bull.  179,  pages  175-6,  except 
that  flakes  were  used  instead  of  bars  of  soap. 


120 


CONNECTICUT   EXPERIMENT   STATION. 


BULLETIN   252. 


Continued  experimentation  in  1923  in  the  orchard  at  the  Ex- 
periment Station  Farm  and  in  the  orchard  at  Conyers  Farm, 
Greenwich,  substantiated  the  results  in  1922  except  for  the  use 
of  fish  oil  soap,  the  results  in  this  case  not  appearing  so  favorable 
as  in  1922,  and  the  foliage  turning  brown  before  the  end  of  the 
summer.  Two  different  counts  were  made  in  both  orchards,  and 
the  results  are  shown  in  Tables  18  and  19. 

Table  18 — Results  of  Spraying  at  Station  Farm. 
Examination  June  21  and  22,  1923. 


Condition 

No. 

Total  No. 

Total  No. 

Total  No. 

Total  No. 

Treatment,                 Date  of 

of 

Leaves 

Eggs 

Live  Mites 

Cast  Skins 

Dead  Mites 

Received               Treatments 

Leaves 

Examined 

Per  100 

Per  100 

Per  100 

Per  100 

Leaves 

Leaves 

Leaves 

Leaves 

1.     Lime-sulphur  May  11 

Nicotine  Sulphate  May  29-31 

Lead  Arsenate . .     June  14 

Kayso  and  Lime    June  26 

Green 

100 

16 

1 

33 

14 

2.     Lime-sulphur 

Lead  Arsenate 

Kayso  and  Lime            " 

Green 

125 

7 

6 

303 

43 

3.     No  treatment       

Green 

100 

606 

190 

306 

281 

Examination  August  22,  1923. 

1.  Lime-sulphur 
Nicotine  Sulphate 
Lead  Arsenate 

Kayso  and  Lime        Green  25  54 

2.  Lime-sulphur 
Lead  Arsenate 

Kayso  and  Lime         Green  25  48 

3.  No  treatment       Slightly 

browned  10  12 


8 

16 
10 


572 

240 
13,580 


Table  19 — Results  of  Spraying  at  Conyers  Farm. 


Treatment 
Received 


Date  of 
Treatments 


1.     Lime-sulphur 
1—50 


May  2 
May  24 
June  26 

2.     Lime-sulphur  May    2 

followed  by  linseed 

oil  emulsion  May  24 


Examination  June  12,  1923. 

Condition  No.  Total  No.  Total  No.     Total  No.  Total  No. 

of  Leaves  Eggs  Live  Mites  Cast  Skins  Dead  Mites 

Leaves       Examined        Per  100        Per  100         Per  100         Per  100 
Leaves         Leaves  Leaves  Leaves 


Green 


225 


130 


June  26 

Green 

100 

39 

61 

71 

88 

3.     Check,  no 

treatment                   

Turning 
brown 

50 

286 

1,220 

1,094 

258 

4.     Lime-sulphur  May    2 
plus  nicotine  sul-  May  24 
phate                      June  26 

Green 

160 

3 

6 

178 

16 

5.    Lime-sulphur 
plus  Kayso  and 
Sulphur                          " 

Green 

210 

11 

26 

227 

25 

6.    Fish  Oil  Soap 

and  Sulphur                   " 

Green 

200 

25 

29 

196 

38 

THE    EUROPEAN    RED   MITE. 


121 


Table  19.     Results  of  Spraying  at  Conyers  Farm — Continued. 


Examination  August  2,  1923. 


Treatment 
Received 


Date  of 

Treatments 


Condition 

of 

Leaves 


1.  Lime-Sulphur 

1—50  Green 

2.  Lime-sulphur 

1 — 50  followed  by 

linseed  oil  emulsion     Green 

3.  Check,  no 

treatment  Brown 

4.  Lime-sulphur 
plus   nicotine   sul- 
phate           Green 

5.  Lime-sulphur 
plus  Kayso  and 

Sulphur  Green 

6.  Fish  oil  soap 

and  Sulphur  Brown 


No 

Leaves 

Examined 


25 


25 


25 


25 


25 


Total  No. 

Eggs 

Per  100 

Leaves 

212 


328 


Total  No.     Total  No.    Total  No. 
Live  Mites  Cast  Skins  Dead  Mites 


Per  100 
Leaves 

44 


168 


20 


140 


32 


25 


Per  100 

Leaves 

592 


5,590 
18,300 


Per  100 
Leaves 

40 


120 


25         1,648 

Notes. 


44         3,476 


8  1,562 

544       10,300 


16 


280 


Table  18.  Insecticides  used  at  the  following  strengths  in  all  tests.  Lime-Sulphur 
1.5  gal.  to  50  gals.;  nicotine  sulphate  .5  pint  to  50  gals.;  Lead  arsenate  1.5  lbs.  to  50  gals.; 
Kayso  .75  lb.  to  50  gals.;  hydrated  lime  1.5  lbs.  to  50  gals. 

Table  19.  Insecticides  used  at  following  strengths.  2. — One  per  cent,  linseed  oil 
emulsion.  4. — Lime-sulphur  1  gal.  to  50  gals.,  nicotine  sulphate  6  oz.  to  50  g^ls.  5. — 
Xime-sulphur  .5  gal.  to  50  gals.,  Kayso  .75  lbs.  to  50  gals.,  sulphur  5  lbs.  to  50  gals.  6. — 
Potash  fish  oil  soap  5  lbs.  to  50  gals.,  sulphur  5  lbs.  to  50  gals. 

Cast  skins  left  upon  the  leaves  gave  a  reliable  index  of  the 
efficiency  of  a  spray  in  1923,  the  total  number  found  indicating 
how  many  mites  had  been  present.  Thus  at  the  Experiment 
Station  Farm,  examination  August  22,  check  trees  showed  twenty 
to  fifty  times  as  many  cast  skins  per  leaf  as  in  the  case  of  trees 
sprayed  with  lime-sulphur.  At  the  Conyers  orchard  the  check 
trees  had  from  six  to  thirty  times  as  many  casts  as  could  be  found 
on  trees  sprayed  with  lime-sulphur.  This  seems  to  be  more  reliable 
than  judging  the  foliage  greenness,  which  may  be  affected  by  a 
number  of  causes.  It  will  also  be  seen  that  no  conspicuously 
greater  control  was  obtained  with  lime-sulphur  to  which  nicotine 
alone  was  added  than  with  lime-sulphur  combinations  containing 
no  nicotine.  Lime-sulphur  combinations  thus  far  have  not  failed 
in  a  single  instance  under  our  observation  to  control  the  red  mite 
successfully  if  applied  according  to  spray  calendar  recommenda- 
tions, especial  attention  being  given  to  early  summer  sprays. 

Mineral  oil  and  linseed  oil  emulsions  are  very  effective  in  killing 
mites — apparently  more  so  than  lime-sulphur  if  the  count  is  made 
shortly  after  the  spray  is  applied.  They  have  given  uniform 
results  of  this  kind  in  every  instance  and  there  is  no  reason  why 
linseed  oil  emulsion  (or  other  safe  spraying  oil)  cannot  be  used  to 
advantage  on  trees  unable  to  stand  commercial  lime-sulphur.     For 


122  CONNECTICUT   EXPERIMENT   STATION.  BULLETIN   252. 

apples  their  use  seems  to  be  needless  in  view  of  more  efficient 
fungicidal  effects  of  lime-sulphur.  Soaps  are  likely  to  vary,  and 
while  their  combination  with  sulphur  may  be  effective  at  times, 
even  this  combination  may  fail  to-  give  good  results.  Probably 
their  continued  effect  is  dependent  upon  heat  as  with  sulphur 
dusts  already  mentioned.  A  field  test  of  three  oil  emulsions  is 
shown  in  Table  20. 


Table  20.     European  I 

Ied  Mite  Control  at 

Conyers  Orchard,  f 

Sprayed  June  25 

,  1923. 

Exp.                Insecticide 
No.                       Used 

Number 
Live  Mites. 

Number 
Dead. 

Per  Cent. 
Dead. 

Possible  Kill 
Per  Cent. 

1.     Sunoco  spraying  oil 
1  part  in  100  parts 
water 

6 

395 

98.5 

98.1 

2.    Linseed  oil  emulsion 
1  gallon  linseed  oil 
1  \i  lbs.  Ivory  soap 
100  gallons  water 

30 

177 

85.5 

82.5 

3.     Schnarr's  insecticide 
1  part  in  100  parts 
water 

28 

412 

93.5 

92.6 

4.     None 

241 

61 

20.1 

0.0 

Notes. 

Trees  in  experiments  1  and  3  sprayed  with  hand  pump  and  rod,  2  with 
gun  and  power  outfit. 

Spray  Burn  Resulting  from  Sprays  Containing 
Lime-sulphur. 

The  main  objection  to  the  use  of  lime-sulphur  solution  has  been 
due  to  burning  of  the  foliage.  Severe  spray  burn  was  noticed  in 
different  sections  of  Connecticut  in  1923  and  notes  upon  the 
probable  cause  are  timely.  As  the  spray  formula  consists  of 
several  compounds,  the  following  possibilities  arise : 

1.  The  cause  of  the  spray  burn  may  be  the  lime-sulphur 
solution — due  to  composition  or  strength. 

2.  It  may  be  due  to  lead  arsenate  alone — due  to  high  water 
soluble  arsenic  content. 

3.  It  may  be  due  to  nicotine  sulphate — especially  combination 
products  with  other  insecticides. 

4.  It  may  be  due  to  a  combination  of  all  of  these  materials 
resulting  in  other  compounds  or  altered  original  compounds  which 
cause  burning. 

5.  Weather  conditions  noticeably  affect  the  degree  of  spray 
burn. 

6.  The  particular  variety  may  be  susceptible  to  spray  injury. 


t  Leaves  collected  immediately  after  treatment  and  examined  the  following  day. 


THE    EUROPEAN    RED    MITE.  123 

Considering  these  causes  in  order,  with  precautions  necessary  to 
avoid  injury,  it  seems  advisable : 

1.  To  reduce  the  strength  of  lime-sulphur  on  tender  varieties 
such  as  Baldwin  from  1 3^  to  50  gallons  to  1  to  50  or  even  1  to  75  in 
the  later  applications. 

2.  To  obtain  a  guarantee  that  the  lead  arsenate  used  shall 
contain  no  more  than  .75%  of  water  soluble  arsenic.  If  large 
quantities  are  purchased  have  the  material  analyzed  for  water 
soluble  arsenic  at  the  Experiment  Station  or  elsewhere. 

3.  Omit  nicotine  sulphate  unless  aphids  are  present  in  the 
orchard. 

4.  Combine  your  sprays  in  the  following  order : 

1.  Lead  arsenate 

2.  Nicotine  sulphate 

3.  Casein  lime 

4.  Lime-sulphur. 

Do  not  allow  sludge  to  collect  in  the  bottom  of  the  spray  tank;  clean 
frequently. 

5.  Do  not  spray  when  the  temperature  or  humidity  is  high. 
It  is  best  to  stop  when  the  temperature  reaches  90  degrees. 

6.  Be  particularly  careful  with  Baldwin  and  other  thin  leaved 
varieties.  If  the  trees  continue  to  be  burned,  use  formula3  con- 
taining lime-sulphur,  casein  lime  and  sulphur  as  follows: 

Water 100  gallons 

Lime-sulphur 1  gallon 

Finely  ground  sulphur 5-10  lbs. 

Casein  lime 1  lb. 

Summary  and  Recommendations. 

1.  The  European  red  mite  passes  the  winter  in  the  egg  stage 
upon  smaller  twigs  and  branches.  Eggs  hatch  in  April  or  May  at 
the  time  fruit  buds  are  turning  pink. 

2.  The  incubation  period  of  the  summer  egg  varies  from  six 
to  thirteen  days,  and  the  adult  develops  in  five  to  ten  days.  The 
preoviposition  period  lasts  from  one  to  seven  days,  but  eggs  are 
usually  laid  within  a  few  days  after  emergence.  Adults  lived  six  to 
nineteen  days  and  adult  females  laid  a  total  of  sixteen  to  thirty- 
four  eggs  during  their  lives.  Winter  eggs  are  sometimes  laid  in 
August;  usually  however  during  September  and  early  October. 
Winter  eggs  are  dark  red,  summer  eggs,  brown. 

3.  This  mite  is  easily  distinguished  from  other  species  in  adult 
and  egg  stage. 

4.  An  infestation  of  50  to  100  mites  per  leaf  is  sufficient  to 
cause  leaves  of  apple  trees  to  turn  brown.  Baldwin  is  the 
variety  most  commonly  injured. 


124  CONNECTICUT  EXPERIMENT   STATION.  BULLETIN  252. 

5.  Enemies  become  numerous  in  July  and  August  and  are  often 
responsible  for  the  disappearance  of  the  red  mite. 

6.  Dry  weather  in  summer  favors  .their  development  and  a  wet 
period  with  frequent  showers  keeps  them  in  check. 

7.  A  definite  spray  schedule  should  be  adopted  in  orchards 
where  mites  are  numerous. 

8.  Lime-sulphur  delayed  dormant  spray  is  not  effective  because 
of  the  late  hatching  of  the  egg. 

9.  Miscible  oils  are  effective  dormant  sprays,  and  with  care  are 
reasonably  safe  in  orchard  work.  Fall  sprays  of  miscible  oil  are 
apparently  ineffective. 

10.  Lime-sulphur,  summer  strength,  sprays  should  be  applied 
early  beginning  with  the  pink  spray,  which  should  be  followed  by 
at  least  two  others  containing  lime-sulphur,  the  latest  being 
applied  the  last  of  June  or  first  of  July. 

11.  Nicotine  sulphate  is  unnecessary  in  the  spray  mixture  so  far 
as  mite  control  is  concerned. 

12.  Soaps,  miscible  oils  and  linseed  oil  emulsion  are  very 
effective  summer  sprays,  but  needless  and  apparently  less  efficient 
in  control  of  fungous  diseases  than  lime-sulphur. 

13.  Care  should  be  exercised  in  applications  of  lime-sulphur 
and  the  precautions  noted  on  page  123  carefully  observed. 

Acknowledgments. 

In  the  course  of  the  work  outlined  in  the  present  paper,  several 
persons  have  aided  materially.  Dr.  W.  E.  Britton,  and  Messrs. 
M.  P.  Zappe,  B.  H.  Walden,  E.  M.  Stoddard  and  G.  E.  Graham 
have  given  invaluable  service.  The  use  of  orchards  belonging  to 
the  Plant  Brothers  at  Branford,  S.  T.  Bradley  of  North  Branford, 
F.  N.  Piatt  of  Milford,  as  well  as  the  Conyers  orchard  at  Green- 
wich, managed  by  Messrs.  G.  A.  Drew  and  H.  B.  Reed,  has  in- 
creased the  scope  of  the  work  immeasurably.  Thanks  are  due 
to  all  persons  in  charge  of  orchards,  without  whose  aid  orchard  field 
work  would  have  been  impossible;  and  to  those  who  have  given 
personal  service  and  advice  throughout  the  period  of  these  in- 
vestigations. 

Literature. 

1.  Caesar,  L. 

1915.    In  Canadian  Entomologist,  57-58. 

2.  DeLong,  D.  M. 

1923.     Results  of  Spraying  and  Dusting  for  the  Control  of  the  Red 
Spider  (Paratelranychus  pilosus). 
In  Journ.  Econ.  Ent.  16:  88-90. 

3.  de  Ong,  E.  R. 

1922.     The  Control  of  Red  Spider  in  Deciduous  Orchards. 
Cal.  Agr.  Exp.  Sta.  Bull.  347. 

4.  Essig,  E.  O. 

1922.     The  European  Red  Mite. 

In  Mo.  Bui.  Cal.  State  Dept.  Agr.  11:  409-411. 


THE   EUROPEAN   RED   MITE.  125 

5.    Ewing,  H.  E. 

1912.     The  Occurrence  of  the  Citrus  Red  Spider  Telranychus  mytilas- 
pidis  Riley  on  Stone  and  Citrus  Fruit  Trees  in  Oregon. 
In  Journ.  Econ.  Ent.  5:  414-415. 


6. 


11. 


1914.     The  Common  Red  Spider  or  Spider  Mite. 
Ore.  Agr.  Exp.  Sta.  Bui.  121. 

7.  Fernald,  H.  T.  and  Bourne,  A.  I. 

1922.  Injury  to  Foliage  by  Arsenical  Sprays. 
Mass.  Agr.  Exp.  Sta.  Bui.  207. 

8.  Flint,  W.  P. 

1923.  Shall  we  Change  our  Recommendations  for  San  Jose  Scale 

Control? 

In  Journ.  Econ.  Ent.  16:  209-212. 

9.  Frost,  S.  W. 

1919.    In  Journ.  Econ.  Ent.  12:  407. 
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1921.     The  European  Red  Mite,  Paratelranychus  pilosus  Can.  &  Fanz., 

in  Connecticut. 

In  Journ.  Econ.  Ent.  14:  355-359. 


1920.  In  Rept.  Conn.  State  Entomologist,  184-189. 

1921.  "  "  "  "  146-152. 

1922.  "  "  "  "  333-338. 

12.  Hamilton,  C.  C. 

1922.  Univ.  Md.  Extension  Service  Information  Card  No.  6. 

13.  Houser,  J.  S. 

1923.  Proc.  Fifty-sixth  Ann.  Meeting  Ohio  Sta.  Hort.  Soc,  56-59. 

14.  McGregor,  E.  A. 

1919.  The  Red  Spiders  of  America  and  a  Few  European  Species  Likely 
to  be  Introduced. 

Proc.  U.  S.  Nat.  Mus.  56:  641-679. 

15.  Stratford,  G. 

1920.  Control  of  Red  Mite  on  Apple  Trees. 

In  New  Zealand  Journal  of  Agriculture  XX:  176-178. 

16.  Tragardh,  Ivar. 

1915.     Bidrag   Till   Kannedomen   Om   Spinnkvalstren    (Tetranychus 
Duf.). 
Med.  nir.  109,  fr.  Cent,  f.-fors,  pa  jordbr.     Entom.  avdel.  n:  r  20. 

17.  Quayle,  H.  J. 

1912.  Red  Spiders  and  Mites  of  Citrus  Trees. 
Cal.  Agr.  Exp.  Sta.  Bui.  234. 

1913.  Some  Natural  Enemies  of  Spiders  and  Mites. 
In  Journ.  Econ.  Ent.  6:  86-88. 

18.  Vinal,  Stuart  C. 

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